Book covers, folders and booklets of the kind described above are already known. They generally comprise a cardboard and/or plastics material, which is provided with a spine and two covers joined thereto via two crease lines, said covers enclosing a plurality of sheets of paper. In producing the blank comprising covers and spine, a sheet or roll of material is cut to the desired format, the blank being provided with two crease lines defining the spine. In order that said sheets of paper shall be attached to the spine, it is coated with a bonding agent or binder, subsequent to which the sheets of paper are pushed into the binder, which is then allowed to harden.
Binders of thermosetting type have begun to be used to rationalize the manufacture of folders and booklets. Such a binder is in a solid state at room temperature, and is supplied in large sheets or rolls from which strips are cut. A strip is attached to the inside of the spine by placing it between the crease lines and thereafter heating it so that the binder melts and adheres to the inside of the spine. When the binder has hardened, the book covers are taken to a binding machine such as the one disclosed in U.S. Pat. No. 4,367,116 together with the pages whch are to be enclosed between the covers, with the edges of the sheets in contact with the strip attached to the inside of the spine. The strip is heated by the machine, the edges of the sheets being surrounded by viscous binder. After cooling the sheets are rigidly attached to the spine.
The above-described method of manufacturing folders or booklets is comparatively effective, but necessitates a plurality of work operations. Furthermore, during the process it is difficult to orient the strip exactly on the inside of the spine between the crease lines, which is necessary if all the sheets along the whole of their length are to make contact with the strip and adhere firmly thereto, and if the crease lines are to be kept free from binder and the covers are to be bent as intended, without any obstruction.
A modification of producing the book covers as described above is disclosed in U.S. Pat. No. 4,367,061 wherein the crease lines are formed in the blank at the same time as the binder is adhered to the spine. The main advantages with this method are that the crease lines are formed and the binder is attached to the spine in one single operation and that the binder will be oriented exactly between the crease lines.
Both the above described known methods, however, require that the binder is in solid state and in the form of a strip, which must be manufactured from large sheets or rolls by cutting. Before then such sheets or rolls must be manufactured by melting binder material and forming it to desired widths and thicknesses which often vary for different sizes of book covers.